Re: [PATCH 0/26] get_user_pages() cleanup

[Christoph Hellwig <hch@infradead.org>]

On Wed, Oct 02, 2013 at 04:27:41PM +0200, Jan Kara wrote:
>   Hello,
> 
>   In my quest for changing locking around page faults to make things easier for
> filesystems I found out get_user_pages() users could use a cleanup.  The
> knowledge about necessary locking for get_user_pages() is in tons of places in
> drivers and quite a few of them actually get it wrong (don't have mmap_sem when
> calling get_user_pages() or hold mmap_sem when calling copy_from_user() in the
> surrounding code). Rather often this actually doesn't seem necessary. This
> patch series converts lots of places to use either get_user_pages_fast()
> or a new simple wrapper get_user_pages_unlocked() to remove the knowledge
> of mmap_sem from the drivers. I'm still looking into converting a few remaining
> drivers (most notably v4l2) which are more complex.

Even looking over the kerneldoc comment next to it I still fail to
understand when you'd want to use get_user_pages_fast and when not.

This isn't meant as an argument against your series, but maybe a hint
that we'd need further work in this direction.

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